Heat exchange fin and the production method thereof

ABSTRACT

A heat exchange fin spacer. The fin may be sandwiched between two plates in a brazed-plate heat exchanger. The fin is based upon a corrugated product having wave legs which, when mounted, define flow channels for a gas to be condensed. The fin has at least one condensed liquid drainage channel on the wave legs and deviation elements that drain the liquid towards at least one lateral edge of the wave legs. The deviation elements are provided with at least one leading edge and/or at least one inclined trailing edge. The invention is suitable for use in the main heat exchanger of an air separation unit.

The present invention relates to a heat-exchange spacer fin intended tobe sandwiched between two plates that define a condensation passage of abrazed-plate heat exchanger, of the type comprising a corrugatedproduct, especially with a corrugation of rectangular cross section,having corrugation legs which, in the fitted state, define flow channelsfor a gas to be at least partly condensed, comprising at least onedrainage channel for liquid condensed on the corrugation element legs,extending along a lateral edge of the corrugation element leg, anddeflection members placed on the corrugation element leg and designed todeflect condensed liquid toward this drainage channel.

The invention applies in particular to the main condenser-reboilers ofdouble air distillation columns, which vaporize liquid oxygen by thecondensation of gaseous nitrogen, to the condenser-reboilers of tripleair distillation columns and to the condenser-reboilers of argoncolumns.

These condenser-reboilers operate for example in thermosiphon mode.

Condenser-reboilers operating in thermosiphon mode comprise an exchangerbody, which is more or less completely immersed in a bath of liquidoxygen. The exchanger body consists of a stack of vertical rectangularplates, of corrugated spacers comprising heat-exchange fins, and ofclosure bars, which define a plurality of first passages and a pluralityof second passages. The first passages are condensation passages for aheating fluid. The second passages are vaporization passages for arefrigerating fluid, which are open at the top and at the bottom and areprovided with corrugated spacer fins along the vertical main direction.The exchanger body furthermore includes heating-fluid inlet and outletboxes which sit on top of the rows of inlet and outlet windows emerginginto the first passages. Liquid oxygen penetrates the second passagesvia the bottom, is heated in these passages up to its bubble point andthen is partially vaporized.

Gaseous nitrogen penetrates the first passages via the top, gives upheat to the oxygen circulating in the second passages and is condensed.Consequently, a film of liquid nitrogen is established on the surface ofthe fin and flows downward. The flow is referred to as a “falling film”.

The resistance to heat transfer, in falling-film condensation, issubstantially proportional to the thickness of the liquid film. Giventhat the resistance varies with the ⅓ power of the flow rate, it rapidlyincreases at the points of nitrogen condensation and thus reduces thecapacity for heat exchange between the gaseous nitrogen and the fin.

The object of the invention is to propose a heat-exchange fin for acondensation passage that has an increased capacity for heat exchange.

For this purpose, the subject of the invention is a heat-exchange spacerfin of the aforementioned type, characterized in that at least onedeflection member has a leading edge and/or a trailing edge that isinclined toward an associated drainage channel.

The spacer fin according to the invention may include one or more of thefollowing features, taken individually or in any other technicallypossible combinations:

-   -   the angle between the leading edges and the general liquid flow        direction is between 5° and 70°, preferably between 10° and 45°;    -   the angle between the trailing edges and the general liquid flow        direction is between 5° and 70°, preferably between 10° and 45°;    -   the deflection members of each corrugation element leg are        designed to drain the liquid toward a single lateral edge of the        corrugation element leg and the deflection members of two        successive corrugation element legs are designed to drain the        liquid toward two opposed lateral edges;    -   the deflection members are designed to drain the liquid        condensed on each of the corrugation element legs toward the two        lateral edges;    -   the corrugation element legs have, over their entire height with        the exception of the regions associated with a drainage channel,        deflection members;    -   the spacer fin comprises corrugation element bottoms and        corrugation element tops and the deflection members comprise        first and second members, the first of which are inclined toward        a drainage channel associated with the corrugation element        bottom and the second of which are inclined toward a drainage        channel associated with the corrugation element top;    -   the successive members of two corrugation element legs consist        only of first members on one of the two corrugation element legs        and only of second members on the other of these two corrugation        element legs;    -   each corrugation element leg comprises a first group of first        successive members and a second group consisting of second        successive members, the first and second members each extending        over substantially the entire height of the corrugation element        legs;    -   said first and said second members are symmetrical with respect        to the mid-line of the corrugation element leg;    -   said first members are offset with respect to said second        members along the general liquid flow direction, especially by        one half of the distance between two successive first or second        members;    -   said first and second members lie opposite each other, one on        one side of the mid-line and the other on the other side        thereof, especially so as to form a chevron;    -   in the unfolded state of the spacer fin, the deflection members        of the corrugation element legs form rows lying parallel to one        edge of the spacer fin and perpendicular to the edges of        corrugation element legs and the deflection members of a row are        identical;    -   the deflection members have a leading edge and a trailing edge        and at least the leading edge and preferably the leading edge        and the trailing edge are at all points inclined and directed        toward the associated drainage channel;    -   the deflection members include a slot which is made in the        corrugation element leg;    -   the deflection members include a projecting part on the surface        of the corrugation element leg or a part set back with respect        to the surface of the corrugation element leg, especially a        dished part;    -   each gas flow channel has on the two lateral faces consisting of        corrugation element legs only projecting parts or, on the two        lateral faces, only parts setback with respect to the surfaces        of these corrugation element legs;    -   two successive deflection members on a corrugation element leg        are separated from each other, along said general liquid flow        direction, by a distance of less than 5 cm, preferably of less        than 20 mm;    -   the drainage channel comprises a strip of continuous material of        the corrugation element leg adjacent to the deflection members        and a strip of continuous material on the corrugation element        top or the corrugation element bottom adjacent to the        corrugation element leg;    -   the general liquid flow direction is substantially identical to        the general fluid flow direction in the gas flow channels;    -   the spacer fin comprises partially offset corrugations and the        distance between two successive offsets has a length of at least        3 mm and preferably of at least 1 cm; and    -   the spacer fin comprises at least two fin parts, each of which        has a different drainage capacity, and the drainage capacity        increases from one fin part to the next fin part in the general        fluid flow direction.

The subject of the invention is also a brazed-plate heat exchangercomprising plates that define, between them, heating passages andpartial or complete condensation passages of flat general shape, andcomprising, in each condensation passage, a heat-exchange spacer fin,and also lateral closure bars, characterized in that at least oneheat-exchange spacer fin is a spacer fin as defined above.

The heat exchanger may constitute a condenser-reboiler of an airdistillation unit.

The subject of the invention is also a process for the manufacture of aheat-exchange fin as defined above, characterized in that it comprisesthe following successive steps:

-   -   parallel rows of deflection members are made in a blank of flat        product, especially sheet metal; and    -   the flat product is plastically bent, forming corrugations, in        such a way that the deflection members of a row are located on        the corrugation element legs.

According to one particular method of implementation, the process ischaracterized in that:

-   -   first branches of the chevron are made in the blank; and then    -   second branches of the chevron are made in the blank.

The invention will be more clearly understood on reading the followingdescription, given solely by way of example and with reference to thedrawings in which:

FIG. 1 shows schematically part of a double air distillation columnaccording to the invention;

FIG. 2 is a sectional view of the condenser-reboiler of this doublecolumn, taken in vertical section in the plane II-II of FIG. 1;

FIG. 3 is a perspective view of part of a heat-exchange fin according tothe invention;

FIG. 4 is a view of a condensation passage of the condenser-reboiler incross section on the line IV-IV of FIG. 2;

FIG. 5 is a side view of the leg of the fin of FIG. 3;

FIG. 6 is a plan view of part of a blank for a fin according to FIGS. 3to 5;

FIG. 7 is a plan view of a blank for a first variant of a fin accordingto the invention;

FIG. 8 is a view of a condensation passage of the condenser-reboilercomprising a fin as in one of FIGS. 7, 9 or 10; and

FIGS. 9 and 10 are views similar to FIG. 5 of a second and a thirdembodiment variant, respectively, of the fin according to the invention;

FIG. 11 is a sectional view of a condensation passage comprising a finin a second embodiment according to the invention.

Shown schematically in FIG. 1 is the intermediate part of a double airdistillation column 1. The shell 2 of the double column, common to themedium-pressure column 3 and to the low-pressure column 4 that issuperposed on it may be seen. The domed upper end wall 5 of the column 3separates the two columns and retains in the bottom of the column 4 abath of liquid oxygen 6. The overhead nitrogen in the column 3 iscondensed by indirect heat exchange with the liquid oxygen in the maincondenser-reboiler 7 of the double column, which is placed in the bottomof the column 4 and is completely immersed in the bath 6.

The condenser-reboiler 7 consists of a parallelepipedal exchanger body8, generally made of aluminum or aluminum alloy, and of four nitrogeninlet/outlet boxes of semicylindrical general shape, two of which areupper inlet boxes 9 and two of which are lower outlet boxes 10.

The body 8 consists of a stack of a large number of vertical rectangularplates 11, all identical. Interposed between these plates are, on theone hand, peripheral closure bars 12 and, on the other hand, corrugatedspacers, namely heat-exchange corrugation elements 13 of verticalprincipal orientation.

The body 8 is assembled in a single operation by furnace brazing, andthe four boxes 9 and 10 are welded to this body.

A large number of flat passages are thus defined between the plates 11,alternately nitrogen condensation first passages 15 and oxygenvaporization second passages 16.

The first passages 15 (FIG. 2) are closed around their entire perimeterby the bars 12, which however leave free, at each longitudinal end, agaseous nitrogen inlet upper window 17 and a liquid nitrogen outletlower window 18.

Each first passage contains four distribution regions, associatedrespectively with the four windows 17 and 18. Each of these regionscontains a distribution corrugation element 19 of horizontal principalorientation. The rest of the first passage 15, which extends over thegreat majority of its surface, is occupied by a heat-exchangecorrugation element 13 consisting of a first heat-exchange spacer fin20. This spacer fin 20 is sandwiched between two plates 11.

Each of the two nitrogen inlet boxes 9 sits on top of a horizontal rowof windows 17. Likewise, each of the two nitrogen outlet boxes 10 sitson top of a horizontal row of windows 18.

The second passages 16 are entirely open on their upper and lower sidesand they are closed on their two vertical sides, over their entireheight, by the closure bars 12. They contain only exchange corrugationelements 13 consisting of a second heat-exchange fin. These fins may beof corrugated sheet metal with a smooth surface.

In operation, gaseous nitrogen, coming from the column 3 via lines 22,is introduced into the first passages 15 via the two boxes 9, isdistributed over the entire length of the first passages by the uppercorrugation elements 19 and condenses on the surface of the firstheat-exchange spacer fins 20. The liquid nitrogen thus obtained, whichis collected in the two boxes 10 by the lower corrugation elements 19,is sent back as reflux into the column 3 via lines 23.

Gaseous nitrogen flows through the condenser-reboiler 7 in a generalnitrogen flow direction V, which in this case is vertical.

Condensation of the nitrogen causes liquid oxygen to vaporize in thesecond passages 16.

FIG. 3 shows, seen in perspective, part of a first heat-exchange spacerfin 20.

This fin 20 comprises a corrugation 24 of rectangular cross section,having a corrugation pitch p₀ and consisting of corrugation elementbottoms 26 and corrugation element tops 28 joined by corrugation elementlegs 30. Each corrugation element leg 30 has two lateral sides 31extending along the corrugation element bottoms 26 or tops 28. As may beseen in FIG. 4, the corrugation element bottoms 26 and corrugationelement tops 28 are fixed over their width l₀ respectively to two plates11 by a layer of braze 32. The corrugation element legs 30 extendbetween these two plates 11 and have a height h₀. Thus, the fin 20 andthe plates 11 define gaseous nitrogen flow channels 34. Typically theheight h₀ is between 3 mm and 10 mm and the width l₀ is between 0.5 mmand 5 mm.

The fin 20 comprises means for draining liquid nitrogen condensed on thesurface of the legs 30 of the fin toward the corners of the fin.

These drainage means comprise, on the one hand, first drainage channels36A and 36B and, on the other hand, members 38 for deflecting condensedliquid toward these drainage channels 36.

Each of the first drainage channels 36A is formed by the junction of acorrugation element leg 30 with a corrugation element top 28, while eachof the first drainage channels 36B is formed by the junction of acorrugation element leg 30 with a corrugation element bottom 28.

For this purpose, each corrugation element leg 30 includes a region 39of continuous material that extends within the corrugation element legfrom the bottom 26 of the corrugation element or from the top 28 of thecorrugation element to the start of the deflection member 38. Thisregion 39, called a ribbon, has a width d_(c) which is at least 0.2 mmand is preferably between 0.5 mm and 1 mm (see FIG. 5).

The bottom 26 and the top 28 of the corrugation element each consist ofa strip of continuous material, devoid of liquid deflection members 38.Consequently, this strip forms a ribbon similar to the ribbon 39.

The first drainage channels 36A, 36B extend along the general nitrogenflow direction V.

Second drainage channels 42A, 42B are formed at points where thecorrugation element legs 30 join the plate 11. These second drainagechannels 42A, 42B are substantially identical to the first drainagechannels 36A, 36B. However, their width is increased by the thickness ofthe corrugation element bottom 26 or corrugation element top 28 and bythe layer of braze 32.

The liquid deflection members 38 consist of a succession of identicalslots 44A, 44B of quadrilateral shape, in this case in the form of aparallelogram, which are provided in the corrugation element legs 30.The slots 44A are inclined toward the drainage channels 36A, 42A, in thegeneral liquid flow direction L, whereas the slots 44B are inclinedtoward the drainage channels 36B, 42B.

Each slot 44A, 44B thus has two long edges, namely the leading edge 46and the trailing edge 48, and two short edges, namely the leading edge50 and trailing edge 52.

The leading edges meet the trailing edges at leading A and trailing Fjunction points. In the case in which the fin 20 is manufactured from aperforated sheet, the edges of the slots are slightly rounded at thepositions of the points A and F.

The width e of the slot, measured in a direction perpendicular to theflow direction L, is less than 2 mm and preferably between 0.1 and 1 mm.

The long 46 and short 50 leading edges are inclined relative to thegeneral liquid flow direction L, toward the drainage channels 36A, 36B,42A, 42B, at angles α and β, whereas the long 48 and short 52 trailingedges are inclined relative to this direction L at angles γ and δ. Inthe case of a parallelogram, α=γ and β=δ (see FIG. 5). The angles α, β,γ and δ are between 5° and 70° and preferably between 10° and 45°, theseangles being measured relative to the general liquid flow direction L.

The angle of inclination α and β of the leading edges 46, 50 is chosenaccording to the flow velocity of the liquid and to the viscosity of thecondensed liquid in such a way that the drops of liquid adhere to theleading edges 46, 50 before being drained away to the point F via thedrainage channels 36A, 36B, 42A, 42B.

In general, the trailing edges 46, 52 are arranged in such a way thatthe trailing junction point F between the long leading edge 46 and theshort trailing edge 52 is, on the one hand, the forwardmost point of thetrailing edge 48, 52 and is, on the other hand, the point on the edge ofthe slot 44A, 44B that is closest to the associated drainage channels36A, 36B, 42A, 42B. Thanks to this configuration, the liquid flowingalong the leading edge 46, 50 is prevented from being deflected towardthe middle of the corrugation element leg 30 from the trailing junctionpoint F.

The leading junction point A is placed as close as possible to thecorrugation element bottom 26 or corrugation element top 28 andpreferably coincides with this bottom or with this top.

In other words, the leading edge 46, 50 is at each point inclined in thedirection L toward the associated drainage channel 36A, 36B, 42A, 42B.Preferably, the leading edge 46, 50 has an upwardly concave or straightshape and the trailing edge 48, 52 is at each point downwardly convex orstraight.

The height h_(f) of each slot 44A, 44B measured in the liquid flowdirection L is chosen so as to weaken the structure of the fin 20 aslittle as possible. The height h_(f) is for example between 0.5 mm and20 mm and preferably between 5 mm and 15 mm.

The distance between two successive slots 44A, 44B is called d_(f). Thisdistance d_(f) is the distance between the trailing point F of a slot44A, 44B and the leading point A of the next slot 44A, 44B. Thisdistance d_(f) is chosen to be less than 5 cm and is preferably lessthan 20 mm.

The pitch between two successive slots 44A, 44B is called p_(f)(=h_(f)+d_(f)). This pitch p_(f) is chosen in such a way that thesurface of the corrugation element leg 30 is just rewetted over itsheight h₀ between two successive slots 44A, 44B. The degree ofperforation, that is to say the ratio of the area of the perforations tothe total area of the fin, is less than 15%.

During operation of the exchanger, a film 56 of liquid nitrogen isestablished, which flows over the surface of the fin 20. The liquid thenencounters the leading edge 46, 50 of a slot 44A, 44B and is deflectedtoward a drainage channel 36A, 36B, 42A, 42B in such a way that a driedregion 44 is established downstream of the slot 44A, 44B. Downstream ofthis slot 44A, 44B is again established, progressively, a liquid film 56by condensation of gaseous nitrogen, which liquid is drained away by thenext slot 44A, 44B.

The slots 44A, 44B reduce the thickness of the liquid film on thecorrugation element leg 30 and consequently the heat-transferresistance. They result, as a consequence, in an increase in theheat-exchange efficiency of the fin.

As is apparent from FIG. 4, during operation, flows of liquid areestablished in the drainage channels 36A, 36B, 42A, 42B. The freesurface for liquid flow in a drainage channel is in the form of apartial cylinder of radius r. The liquid flowing in the drainagechannels 36A, 36B, 42A, 42B is prevented from leaving the latter by thecapillary forces acting on the liquid. The drainability of the drainagechannels is high owing to the fact that the radius r of the free surfacefor the liquid varies as the ¼ power of the liquid flow rate in thedrainage channel in question.

FIG. 6 shows a lower part of a blank F used to manufacture the fin 20.

The blank F has rows R_(p) of slots 44A and 44B in regions correspondingto the corrugation element legs 30. These rows R_(p) extendperpendicular to the lower edge B of the blank F.

The slots also form rows R extending parallel to the lower edge B andperpendicular to the lateral edges 31 of the corrugation element legs30.

The pattern formed by the slots 44A, 44B is identical on all thecorrugation element legs 30 and is reproduced with a periodicity p_(h)identical to the folding periodicity p_(p).

Thus, a single punch can be used to manufacture the slots 44A and 44Band this punch is driven synchronously with the tool for folding theblank.

FIG. 7 shows part of a blank of a first variant of a spacer finaccording to the invention.

Only the differences from the aforementioned fin will be described.

The blank F has, in each region corresponding to a corrugation elementleg 30, first groups G1 of five successive first slots 44A and secondgroups G2 of five successive second slots 44B. The first slots 44A areinclined toward one side of the corrugation element leg 30, whereas thesecond slots 44B are inclined to the other side thereof.

The two groups G1, G2 are separated from each other by a distance d_(g)of between 0.5 mm and 5 cm.

Each corrugation element leg 30 includes two ribbons 39 of continuousmaterial, which are associated with the two lateral edges 31 of thecorrugation element leg 30 and are adjacent to the bottom regions 26 ortop regions 28.

Each slot 44A, 44B lies between these two ribbons 39.

During operation, the slots 44A deflect the liquid toward an edge of thecorrugation element leg 30, while the slots 44B deflect the liquidtoward the other edge of the leg (see FIG. 8).

FIG. 9 shows a second variant of the fin 20 according to the invention.This figure corresponds to the view in FIG. 5. Analogous elements bearidentical references.

The liquid deflection members 38 are formed by a succession of firstslots 44A and second slots 44B. The first and second slots lie on eachcorrugation element leg 30 on either side of a mid-line M-M of said leg.

This line M-M lies parallel with the liquid flow direction L, atmid-distance between the corrugation element top 28 and the corrugationelement bottom 26 of the fin 20.

The first slots 44A are inclined to the mid-line M-M toward thecorrugation element tops 28, whereas the second slots 44B are inclinedtoward the corrugation element bottoms 26. The first slots 44A and thesecond slots 44B are symmetrical in shape with respect to the mid-lineM-M.

The trailing junction point F of each slot 44A, 44B is located at adistance d_(c) from the top 28 and from the bottom 26, respectively.This fin 20 includes first drainage channels 36A, 36B on both sides ofeach corrugation element leg 30.

The leading junction point A of each slot 44A, 44B lies on the line M-M.Thus, substantially the entire width of the leg 30 is provided withdrainage slots 44A, 44B.

During operation and as shown in FIG. 8, the liquid is deflected towardthe top 28 and the bottom 26 associated with each leg 30, toward thedrainage channels 36A, 36B and 42A, 42B.

Each of the first 44A or second 44B slots is offset relative to thefirst or second following slot by a distance p_(f).

In other words, the pattern formed by the combination of two slots 44A,44B is repeated after a distance p_(m).

The distance d_(f) between the point F of a slot 44A, 44B and the pointA of a following slot 44B, 44A is between 0 mm and 2.5 cm.

The first slots 44A are offset relative to the second slots 44B by adistance p_(f)=p_(m)=/2 in the flow direction L.

This offset results in considerable strength of the fin 20 in thedirection of the corrugation element leg 30.

FIG. 10 shows a third variant of the fin according to the invention.

The slots 44 of this fin 20 are substantially in the form of a chevron.The point A of the chevron lies on the mid-line M-M and is directedupstream relative to the general liquid flow direction L.

The two arms 44A, 44B of the chevron have a shape substantiallyidentical to the first 44A and second 44B slots of the first variant ofthe fin 20. The difference is that the leading edge 46A, 46B of each armis straight from the leading point A as far as the trailing point F.During operation, the liquid flow is established on both sides of eachcorrugation element leg 30, in a similar manner to that of the secondvariant (FIG. 8).

Each chevron-shaped slot (FIG. 10) is either cut out by a correspondingchevron-shaped punch, or by two separate punches, each of whichcorresponds to one arm 44A, 44B of a slot 44. In the latter case, theslot 44 is cut out in two successive steps.

FIG. 11 shows a second embodiment of a fin according to the invention.This view corresponds to the view of FIG. 4, but shows only onecorrugation element.

The difference is that the liquid deflection elements 38 consist ofdished parts 60 in the surface of the corrugation element legs 30. Thedished parts 60 form, on one side of the corrugation element leg, agroove 62 and on the other side of the corrugation element leg a rib 64.

The shape and the geometrical configuration of the dished parts 60 inside view are identical to those of the slots 44A, 44B of theembodiments of the fin described above.

The depth of drawing f_(e) of the dished part 60 is less than one halfof the corrugation element width l_(o) and is, for example, between 0.1mm and 0.25 mm.

The heat-exchange fin according to the invention can be easilymanufactured from a flat product, for example a sheet of aluminum.

The slots 44, 44A, 44B are then produced by perforation.

Alternatively, the dished parts 60 are formed by drawing before the flatproduct is folded. Preferably, the drawing is carried out on only oneside, so that the grooves 62 lie on one side of the blank. In this case,each channel 34 has, on both its side faces, formed by the corrugationelement legs 30, either deflection grooves 62 or deflection ribs 64.

As a variant, the deflection members 38 are manufactured on a fin of the“serrated” type, i.e. a fin having corrugations with a partial offset.In this case, the length of the corrugations in the general liquid flowdirection must be large enough to wet the surface of the leg. The lengthof the corrugation, also called the serration length, in the liquid flowdirection L must be at least 3 mm and preferably at least 1 cm.

The fin may also be used in a heat exchanger in which a gas mixtureflows through the cooling passages and in which a fraction of themixture is condensed.

Again as a variant, the fin may consist of two or more fin parts placedone after another in the general liquid flow direction. In this case, itis advantageous for the drainage means 36A, 36B, 38 to have a differentdrainability from one fin part to another and for the drainability toincrease from one fin part to the next fin part in the drainage fluidflow direction. An example of such a fin is a spacer fin that comprisesa first fin part provided with drainage channels 36A, 36B and withdrainage members 38 and a second fin part, which is located downstreamin the liquid flow direction L, comprising smooth corrugation elementlegs 30.

1-25. (canceled)
 26. An apparatus which may used as a heat exchangerspacer fin comprising: a) a corrugated element with a cross sectiondefined by corrugation legs; b) flow channels to condense a gas, saidflow channels defined by said legs; c) at least one drainage channel,for liquid condensed on said legs, extending along a lateral edge ofsaid leg; and d) deflection members located on said legs, wherein saiddeflection members deflect said liquid toward said drainage channel,said deflection members further comprising at least one member selectedfrom the group consisting of: 1) a leading edge inclined toward saiddrainage channel; and 2) a trailing edge inclined toward said drainagechannel.
 27. The apparatus of claim 26, wherein said cross section isrectangular.
 28. The apparatus of claim 26, wherein: a) each saiddeflection member drains said liquid toward a single lateral edge ofsaid corrugation leg; and b) said deflection members of two successivecorrugation legs drain said liquid toward two opposed lateral edges. 29.The apparatus of claim 26, wherein said deflection members drain saidliquid toward both lateral edges.
 30. The apparatus of claim 26, furthercomprising corrugation legs wherein: a) deflection members are locatedover the entire height of said corrugation legs; and b) no deflectionmembers are located on the region associated with said drainage channel.31. The apparatus of claim 26, further comprising: a) a corrugationelement top; b) a corrugation element bottom; c) at least one firstdeflection member, wherein said first member is inclined toward saiddrainage channel associated with said element bottom; and d) at leastone second deflection member, wherein said second member is inclinedtoward said drainage channel associated with said element top.
 32. Theapparatus of claim 31, wherein: a) each said deflection member drainssaid liquid toward a single lateral edge of said corrugation leg; b)said deflection members of two successive corrugation legs drain saidliquid toward two opposed lateral edges; and c) said deflection membersof two adjacent corrugation legs consist of: 1) only said first memberson the first of said corrugation legs; and 2) only said second memberson the second of said corrugation legs.
 33. The apparatus of claim 31,wherein: a) said deflection members drain said liquid toward saidlateral edges; b) said first members and said second members extend oversubstantially the entire height of said corrugation leg; and c) eachsaid corrugation leg further comprises: 1) a first group consisting ofadjacent first members; and 2) a second group consisting of adjacentsecond members.
 34. The apparatus of claim 31, wherein said first andsaid second members are symmetrical with respect to a mid-line of saidcorrugation leg.
 35. The apparatus of claim 34, wherein said firstmembers are offset from said second members by about one half thedistance between two adjacent said first or said second members.
 36. Theapparatus of claim 35, wherein said offset is with respect to thegeneral liquid flow direction.
 37. The apparatus of claim 34, whereinsaid first and said second members are oriented opposite each otheralong said mid-line.
 38. The apparatus of claim 37, wherein said firstand said second members form a chevron shape.
 39. The apparatus of claim31, wherein the orientation of said deflection members is such that,when said apparatus is unfolded, said deflection members comprise rows,wherein: a) said rows are parallel to an edge of said apparatus; b) saidrows are perpendicular to edges of said corrugation leg; and c) saiddeflection members of a said row are identical.
 40. The apparatus ofclaim 31, wherein said deflection members further comprise: a) a leadingedge, wherein said leading edge is at all points inclined and directedtoward said associated drainage channel; and b) a trailing edge.
 41. Theapparatus of claim 40, wherein said trailing edge is at all pointsinclined and directed toward said associated drainage channel.
 42. Theapparatus of claim 31, wherein said deflection members further comprisea slot in said corrugation leg.
 43. The apparatus of claim 31, whereinsaid deflection members comprise at least one member selected from thegroup consisting of: a) a projecting part on the surface of saidcorrugation leg; and b) a set back part with respect to said surface.44. The apparatus of claim 43, wherein said set back part comprises adished part.
 45. The apparatus of claim 43, wherein all said deflectionmembers for said flow channel are of said projecting part type.
 46. Theapparatus of claim 43, wherein all said deflection members for said flowchannel are of said set back part type.
 47. The apparatus of claim 31,wherein the distance between adjacent deflection members, in the generalliquid flow direction, is less than about 5 cm.
 48. The apparatus ofclaim 47, wherein said distance is less than about 20 mm.
 49. Theapparatus of claim 31, wherein said drainage channel further comprises:a) a continuous strip of material from said corrugation leg adjacent tosaid deflection members; and b) a continuous strip of material on atleast one member selected from the group consisting of: 1) saidcorrugation element top adjacent top; and 2) said corrugation elementbottom.
 50. The apparatus of claim 31, wherein the general liquid flowdirection is substantially the same as the general fluid flow directionin said gas flow channels.
 51. The apparatus of claim 31, furthercomprising partially offset corrugations wherein the distance betweenadjacent said offsets is at least about 3 mm.
 52. The apparatus of claim51, wherein said distance is at least about 1 cm.
 53. The apparatus ofclaim 31, further comprising at least two fin parts wherein: a) eachsaid fin part has a different drainage capacity; and b) said capacityincreases from one fin part to the next fin part in the general fluidflow direction.
 54. An apparatus which may be used as a brazed-plateheat exchanger comprising plates that define heating passages andcondensation passages, said condensation passages comprising: a) lateralclosure bars; and b) at least one heat exchange space fin, said fincomprising: 1) a corrugated element with a cross section defined bycorrugation legs; 2) flow channels to condense a gas, said flow channelsdefined by said legs; 3) at least one drainage channel, for liquidcondensed on said legs, extending along a lateral edge of said leg; and4) deflection members located on said legs, wherein said deflectionmembers deflect said liquid toward said drainage channel, saiddeflection members further comprising at least one member selected fromthe group consisting of: i) a leading edge inclined toward said drainagechannel; and ii) a trailing edge inclined toward said drainage channel.55. The apparatus of claim 54, wherein said condensation passagesfurther comprise at least one member selected from the group consistingof: a) partial condensation passages; and b) complete condensationpassages.
 56. An apparatus which may be used as a condenser-reboiler ofan air distillation unit comprising a brazed-plate heat exchangercomprising plates that define heating passages and condensationpassages, said condensation passages comprising: a) lateral closurebars; and b) at least one heat exchange space fin, said fincomprising: 1) a corrugated element with a cross section defined bycorrugation legs; 2) flow channels to condense a gas, said flow channelsdefined by said legs; 3) at least one drainage channel, for liquidcondensed on said legs, extending along a lateral edge of said leg; and4) deflection members located on said legs, wherein said deflectionmembers deflect said liquid toward said drainage channel, saiddeflection members further comprising at least one member selected fromthe group consisting of: i) a leading edge inclined toward said drainagechannel; and ii) a trailing edge inclined toward said drainage channel.57. The apparatus of claim 56, wherein said condensation passagesfurther comprise at least one member selected from the group consistingof: a) partial condensation passages; and b) complete condensationpassages.
 58. A method of condensing a gas comprising a heat exchangerwherein said heat exchanger comprises a brazed-plate heat exchangercomprising plates that define heating passages and condensationpassages, said condensation passages comprising: a) lateral closurebars; and b) at least one heat exchange space fin, said fincomprising: 1) a corrugated element with a cross section defined bycorrugation legs; 2) flow channels to condense a gas, said flow channelsdefined by said legs; 3) at least one drainage channel, for liquidcondensed on said legs, extending along a lateral edge of said leg; and4) deflection members located on said legs, wherein said deflectionmembers deflect said liquid toward said drainage channel, saiddeflection members further comprising at least one member selected fromthe group consisting of: i) a leading edge inclined toward said drainagechannel; and ii) a trailing edge inclined toward said drainage channel.59. The method of claim 58, wherein said condensation passages furthercomprise at least one-member selected from the group consisting of: a)partial condensation passages; and b) complete condensation passages.60. A method of manufacturing the apparatus of claim 28, comprising: a)making parallel rows of said deflection members in a blank of flatproduct; and b) bending plastically said product to form corrugationswherein said deflection members of a said row are located on saidcorrugation legs.
 61. The method of claim 60, wherein said product issheet metal.
 62. A method of manufacturing the apparatus of claim 38,comprising: a) making parallel rows of said deflection members in ablank of flat product; b) creating the first branches of said chevron insaid blank before creating the second branches of said chevron in saidblank; and c) bending plastically said product to form corrugationswherein said deflection members of a said row are located on saidcorrugation legs.